Not sure, so here's some speculation:

15 & 16 is permanenet vs switched +12V. Permanent is just that; always on (like the HU memory wire) while the switched is 12V only while the car is on. Now, if these pins are inputs or outputs is unclear, but my guess is outputs. I'd take a multimeter to them with the HU still connected to the main wire bundle of the car and measure them to make sure.

17 & 18 are probably digital vs analog ground (bus <-> digital, AF <-> Audio Frequency). Could of course be that Renault/Blaupunkt uses entirely different terminology than I would expect....

This page, http://www.bluespot.co.uk/cables.asp, has some Blaupunkt adaptors.
Here too: http://www.caraudiodirect.co.uk/shop/acatalog/CAD_Accessories_252.html

Might be worth talking to them, and see if any of those fits your HU.

/Michael